At present, since the electric drill in the market is just used to clamp a drill head for drilling holes and openings on hard walls, its function is single. Adapters for an electric drill have already been reported. Patent document ZL200810021948.X has disclosed a multifunctional adapter for an electric drill comprising a gearing. The gearing comprises a rocking rod, a swing rod, a sliding rod and a chuck, which are successively connected. One end of the rocking rod is tightly inserted into a mounting hole on the drill head of the electric drill. The rotary movement of a motor shaft of the electric drill is converted to the linear reciprocating movement of the chuck through the gearing. Cutters mounted on the chuck can be saw blades, blades, files and the like to make the electric drill function as electric tools such as electric saws, electric files and the like. In this patent, the rotary movement of the electric drill is converted to the linear reciprocating movement through the rocking rod and the swing rod. One end of the rocking rod is a shaft connected to the mounting hole on the drill head of the electric drill, and the other end of the rocking rod is provided with an inclined plane with a connecting shaft. The upper end of the swing rod sheathes on the connecting shaft and the lower end of the swing rod is connected to the sliding rod. The rotation of the rocking rod is driven by the rotation of the electric drill. The circular rotation is converted into a cone-shaped rotation of the connecting shaft by the presence of the inclined plane. The upper end of the swing rod rotates relative to the connecting shaft, and the lower end is fixed on a straight line to swing from side to side, thus making the sliding rod move straightly and reciprocatingly. The connection between the rocking rod and the shell in the patent is realized by one bearing. Such that when the rocking rod is driven by the electric drill to rotate at a high speed, the irregular rotation of the inclined plane makes the conversion device shake a lot, which is inconvenient for operating. The joint between the inclined plane and the connecting shaft also suffers a great radial shear force and torque, so that it is easy to be broken after being used for a long time.